Looking for a standard set of 5C collets and hex block (dodecagon would be great), no preference on brand. Or some indexing plates I could use to make a custom index fixture. I want to cut some splined shafts and collars, but not exactly sure how I'm going to do it yet. Probably single-point broach using my mill spindle, but my rotary table isn't up to the task until I fix the brakes and slop.

Yeah, the first couple things are relatively straight forward. I already have a 5C spin indexer, but only a handful of random collets. Several of the things I need to do are a fair bit large though... 24 splines in a ~2" bore of a ~5" flange and 6 notches for a ~3" castellated nut. Easy to divide into 360 for the spin indexer, but hard to hold with a 5C collet. I also want to try cutting some custom gears at some point and those will definately not be easily dividable. So I was kind of leaning towards some indexing plates, I could build a base with spindle and mount one of my 4-jaw chucks to it.

If you can find a chuck that will hold your work piece, you can make a 1" spigot to go on the back of it, then use that in a 1" collet. That would give you the ability to hold anything the chuck can hold in your spindex.

Dave Gingery wrote a book on making your own dividing head. That might give you some good ideas on how to make one. There is also the "Workshop practice series" book "dividing". I just got a copy, but have not read it yet. WPS books have a lot of old-school methods in them and probably have a quick and easy way to divide.

If you are using the holes in the plates as your divisions, remember that any error in the plate transfers one-to-one with your work piece. The advantage of a dividing head with a 40:1 worm is that if the hole is off by 1 minute of arc, the work is only affected one fortieth of it.